[lttng-dev] Building URCU in a Cygwin 64 environment

[sboisvert@gydle.com (Sebastien Boisvert)]

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Hi Jonathan,

Thank you for looking into this. I appreciate.

It sounds like I have a solution in hand to continue. That's great.

I just read the text in the web page referenced by the link [1] that you kindly provided to me.
This is interesting. Now I know a little bit more about this.

So, Linux can have 'chains of dependencies of potentially infinite length' whereas Windows
is limited to shared library DLL files that can not depend on other DLL files; knowing the dependencies
is the job of a .exe file and these dependencies must be known at link time.

TIL

+1

On 05/31/2016 10:47 AM, Jonathan Rajotte Julien wrote:
> Hi Sebastien,
> 
> I'll simply move the conversation here (from IRC) to have an archive of it.
> 
> On 2016-05-31 09:39 AM, Sebastien Boisvert wrote:
>> Hi,
>>
>> I am in the process of writing a blog article on the use of the LTTng-UST userspace event tracer on Windows.
>>
>> I am building urcu and LTTng-UST in a Cygwin 64 environment. Then, I plan to use LTTng in Visual Studio Community, so I mostly need headers (.h) and shared libraries (.dll).
> 
> Nice!
> 
>>
>> When I am building urcu (0.9.2), I get this message:
>>
>> libtool: link: warning: undefined symbols not allowed in x86_64-unknown-cygwin shared libraries
> 
> This seems related to a Windows restriction regarding inter-library dependencies [1], the relevant part:
> 
> "Some platforms, such as Windows, do not even allow you this flexibility. In order to build a shared library, it must be entirely self-contained or it must have dependencies known at link time (that is, have references only to symbols that are found in the .lo files or the specified ‘-l’ libraries), and you need to specify the -no-undefined flag. By default, libtool builds only static libraries on these kinds of platforms."
> 
> Looks like the -no-undefined might be a good start judging from this patch I found for the urcu cygwin port in yacp [2].
> 
> Cheers!
> 
> [1] https://www.gnu.org/software/libtool/manual/libtool.html#Inter_002dlibrary-dependencies
> [2] https://github.com/fd00/yacp/blob/master/userspace-rcu/userspace-rcu-0.8.7-1bl1.src.patch
>>
>> The immediate consequence seems to be the absence of .dll files in the urcu build that I am generating. Otherwise, the build contains static library files and headers.
>>
>> However, I suppose that the .a static library files also have undefined symbols as I am getting linking issues when building LTTng-UST.
>>
>> Do you have a clue of what may be the issue here ? Otherwise, I will continue my investigation and get around the issue eventually.
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>